The buyers, also including Stone Point Capital and Edmond de Rothschild Group, will pay $15.55 a share, 19% more than Duff & Phelps' closing price on Dec. 28.

The transaction is expected to be completed in the first half, the companies said in a statement Dec. 29.

The group of buyers will help Duff & Phelps continue its international expansion, according to the statement. Revenue at the 80-year-old firm, which also provides financial advisory services, is predicted to rise 17% this year to $465.8 million, the average of analysts' estimates compiled by Bloomberg.

The Duff & Phelps merger agreement provides for a “go-shop” period ending Feb. 8, during which the company can solicit and receive alternative proposals. Duff & Phelps would pay a breakup fee of about $6.65 million if it gets a higher bid and ends the agreement before March 8.